Optical microcavities are resonators that have at least one dimension (herein typically the effective optical length of the cavity) on the order of a single (or at most a small number, e.g., 2 or 3) optical wavelength(s). It has been recognized that such resonators not only are interesting for fundamental research purposes but also hold technological promise for constructing novel kinds of light emitting devices. See, for instance, H. Yokoyama, Science, Vol. 256, pp. 66-70, which inter alia discloses a microcavity structure that contains a dye solution (FIG. 6). See also Y. Yamamoto et al., Physics Today pp. 66-73, June 1993. Possible applications of microresonator light emitting devices are, for instance, in the fields of flat panel displays, optical interconnects, optical fiber communications and LED printing.
At least some technological fields (e.g., color flat panel displays) require an array of light sources, some of which emit light of one color and some of another. Typically, such arrays are tri-color, e.g., red, green and blue, in order to achieve full color capability. In one exemplary known type of three-color flat panel display, an LED display, this is achieved through provision of three different types of LED. See, for instance, K. Murata, Display Devices, pp. 47-50, 1992, incorporated herein by reference.
Although the prior art knows flat panel LED color displays, the known LED displays are not entirely satisfactory, as evidenced by the fact that such displays are not yet widely used. For instance, prior art displays typically are difficult to manufacture. Thus, a new type of LED color display that is potentially easy to manufacture would be of considerable interest. This application inter alia discloses a novel multicolor array of light sources that can advantageously be used in, e.g., a color display that potentially can be more readily and economically manufactured than some prior art color displays.
It is known that a microcavity device that comprises an organic thin film sandwiched between two mirrors can have interesting optical properties. See, for instance, N. Takada et al., Applied Physics Letters, Vol. 63(15), pp. 2032-2034, and T. Nakayama et al., Applied Physics Letters, Vol. 63(5), pp. 594-595, Aug. 2, 1993. The latter inter alia discloses significant narrowing of the electroluminescence (EL) spectrum of a 50 nm thick tris (8-hydroxyquinolinol) aluminum (Alq) layer between two appropriately spaced mirrors, as compared to such a film that is not between two mirrors. (See FIG. 6 of the reference, which shows a large peak at 495 nm and a very small peak at 660 nm). The reference also discloses that the microcavity contained a triphenyl diamine derivative (TAD) hole transport layer and an indium tin oxide (ITO) transparent electrode layer.